Sealed batteries such as lithium ion secondary batteries are utilized in various fields, e.g., electronic devices such as mobile phones and personal computers, and vehicles such as hybrid vehicles and electric vehicles. In particular, the lithium ion secondary batteries have high energy density and thus are preferably mounted in various kinds of devices.
One example of a method for manufacturing such a sealed battery is known as a method described below. Specifically, a power generating element (an electrode body) including a positive electrode sheet having positive active material and a negative electrode sheet having negative active material is housed in a battery case body made of metal and then a battery case is sealed (hermetically closed). Subsequently, an electrolyte is injected into the battery case through a liquid inlet provided in the battery case, impregnating the power generating element. Then, the liquid inlet is temporarily closed with an inlet plug (a sealing member).
Herein, a battery just fabricated (a battery assembly) is uncharged. Thus, this battery assembly is subjected to initial charge. The initial charge represents first charging to the fabricated battery. The initial charge will cause gas generation in the battery, resulting in an increase in internal pressure of the battery. Therefore, after the initial charge, the battery has to be released from the hermetically closed state once to release the gas.
This gas release (degassing) is performed by forming a degassing path allowing communication between inside and outside of the battery case via the liquid inlet provided in the battery case. After completion of degassing, the degassing path is sealed to bring the inside of the battery case into a hermetically closed state again. In this way, a sealed battery is produced.
A conventional art document related to the above type of battery manufacturing method is for example shown in Patent Document 1 listed below. In the technique disclosed in Patent Document 1, temporary sealing is performed by welding a film to a portion surrounding a liquid inlet of a battery case. Then, the film is cut or torn open to form a degassing path, thereby carrying out degassing. After degassing, another film is welded to close up the degassing path for second temporary sealing and further a metal member is welded (joined) from outside of the films for final sealing. According to this battery manufacturing method, in which the liquid inlet of the battery case is closed with the films, a pressure sealing property in a temporarily sealed state could be sufficiently ensured.